1. Field of the Invention
The present invention is related to the field of medical imaging. More specifically the invention is related to the use of ultrasound for the evaluation of esophageal function, in particular by monitoring a food bolus via non-invasive means.
2. Prior Art
Publications and other reference materials referred to herein are incorporated herein by reference in their entirety and are numerically referenced in the following text and respectively grouped in the appended Bibliography which immediately precedes the claims.
The esophagus propels a swallowed bolus from the oropharynx to the stomach by means of rhythmic peristaltic waves. Normal function of the esophagus resides in the quality, in the amplitude, in the direction, and in the exact synchronized timing of these waves. The term “esophageal function” is herein taken to refer to the characteristics of the peristaltic motion or waves provided by the esophagus during swallowing and reflux, and thus the term “esophageal function parameter” relates to any suitable parameter that represents such motion. Thus, according to the present invention, the esophageal function parameters may be conveniently expressed as at least one of, and preferably all of the following:—propagation direction, inter-boli time and space intervals, velocity and acceleration of peristaltic waves. Preferably the boli are liquid, and thus substantially incompressible, and thus the boli propagation, inter-bolus time interval, and velocity are closely related to the equivalent peristaltic wave characteristics of the esophageal wall.
The functioning of the esophagus has been extensively studied using various methods, among them qualitative measurements (including barium swallow, esophageal scintiscanning, and ultrasound) and quantitative assessments (such as pH-metry and manometry). None of the methods used to date satisfies optimal requirements of safety, efficacy and non-invasiveness. For example, the “gold standard” for evaluating the esophagus is manometry [1,2], which uses continuously perfused low-compliance catheters. Manometry examinations evaluate motility waves through several preset manometric windows and therefore can provide only indirect measurement of the esophageal function as defined above. This procedure requires either the cooperation of the patient, so that regulated swallows may be registered, or a prolonged measurement as was made in a study in premature infants [3]. Especially with children, cooperation is difficult to obtain and sedation is usually needed. Moreover, there is no certainty that the mere insertion of a catheter and the continuous fluid perfusion do not alter the basic functions of the esophagus.
Barium swallow followed by radiography of the upper gastrointestinal tract is non-specific and inconclusive. It also involves X-ray radiation and major discomfort to the patient. Moreover, these methods do not allow repetition of the test in different conditions and thus preclude the assessment of anti-reflux medication or other therapeutic approaches.
Ultrasound is a bedside non-invasive and safe modality. A study using ultrasound can be performed during regular meals, does not require the patient's cooperation and may be repeated as necessary for follow-up or for the evaluation of medical treatment. Nevertheless, up to the present time, its application to qualitative assessment has not been possible.
Takebayashi [10] compared manometry measurements in adults suffering from progressive systemic sclerosis to Doppler measurements after swallowing soda water. As the study included adults only, it was anatomically limited to the cervical esophagus. Attempts to measure transit-time using a stopwatch failed, due to the short segment checked and to the low velocity of soda water. Beyond these limitations, Doppler ultrasound was found to be an effective means in the evaluation of motility in differentiating the normal from the pathologic esophagus in this very limited region of interest.
Gomes et al [7] compared the use of ultrasound, barium swallow and endoscopic studies in 300 children suffering from severe vomiting due to diaphragmatic hernia. The study proved the efficacy of ultrasound in regards to anatomic evaluation and patency of the lower esophageal sphincter, but did not include motility evaluation.
Hirsch et al [8] published in 1996 a study comparing the sensitivity of ultrasound and color Doppler versus pH-metry, which is considered the most sensitive test for evaluating gastro-esophageal reflux. In this study, the subject's stomach was filled with tea. The filling was done in a short time, in order to minimize the amount of gastric emptying, and then the refluxes were measured. In the case of some of the subjects of the study, the esophagus was bypassed by the use of a nasogastric tube to fill the stomach. Thus the study was focused on reflux and was not at all directed at evaluating the esophagus function neither qualitatively nor quantitatively, but rather preferred to bypass the esophagus altogether in some cases. In any case the technique employed was inappropriate for quantification of reflux velocities, as discussed in the paper.
A recent study by Jang et al [9] addressed the same issue but again provided qualitative data only on gastroesophageal reflux.
The search for an optimal method to use ultrasound techniques to evaluate the esophagus is an ongoing quest. In the prior art, conventional Doppler techniques, which are based on high motion or flow velocity measurements and low amplitude signals from the red blood cells, focus exclusively on body parts such as tissues, organs and blood vessels. For example, EP 880937 describes an ultrasonic diagnostic imaging method for tracking a characteristic (such as a tissue boundary) of moving tissue in a body, using a Doppler technique. Such methods are not considered suitable in the prior art for qualitative measurements of the esophagus function primarily due to the poor resolution of this organ with respect to surrounding tissue. Such methods would also be considered in the prior art to be unsuitable for monitoring a swallowed bolus because of the high acoustic backscattering and low velocity propagation associated therewith. While color sonography has been used to detect and “qualify” reflux episodes, no non-invasive method exists which quantifies and characterizes the esophageal function.